Mechanical Engineering, bridge bearings, structural engineering Specialists In Structural Movement Control
Mechanical Engineers Specialising In Structural Movement Control
Shutter Service
A large percentage of these vehicles are heavy goods vehicles, which impose the highest loading on the roller shutter joint link plate trains in lanes one and two. When it first opened, the bridge carried a six-lane dual carriageway — three lanes in each direction - plus hard shoulders. Since the addition of extra capacity more than a decade ago, this heavily-trafficked structure which is part of the M5 motorway now carries an eight-lane dual carriageway over the River Avon in Bristol.
Regular planned maintenance of the structure includes refurbishment of the unusual roller shutter expansion joint arrangement. This is made up of 40 link plate trains that are seated on a slide track, mounted on a curved slide box and fixed to the bridge deck at one end by an anchor plate. A tongue plate on the adjacent bridge deck completes the arrangement. As it is the only longitudinal movement joint on the entire bridge, it must accommodate up to 850mm of movement under service conditions, and a sizeable 1.22m at ultimate limit state.
While the main features and movement principles of this type of expansion joint are fairly common, the roller shutter joint on the Avonmouth Bridge has differences that create specific challenges when it comes to planning and delivering the maintenance and refurbishment works. Access is a major issue, with the joint being located almost at the centre of the 20-span structure, some 30m above the ground and between the River Avon and the Severn Beach railway line. The location is awkward for monitoring purposes; access from beneath is not possible as the underslung permanent bridge gantry cannot move past the expansion joint gap.
Traffic has increased over the last few decades, in particular after a five-year bridge strengthening programme which was completed in 2000, and the widening works completed in 2004 which added an extra lane in each direction; this rise in traffic has significantly increased loading on the structure as well as accumulation of detritus in the joint. Ekspan is currently employed by Skanksa, the maintenance contractor and managing agent for Highways England Area 2, on a framework contract, to carry out maintenance and refurbishment works on the various plate train sections of the joint within the lanes where traffic flow and loading is the greatest, on both the northbound and southbound carriageways. Over time the constant impact loading from heavy traffic creates wear in the feet on the underside of the plate trains. When the feet under the plate trains are worn, they no longer sit level on the slide track, causing the joint to rock and transfer loads into the bridge deck. In addition there is substantial wear on the pins and bushes that connect the plate trains of the roller shutter joint.
Ekspan has a planned two-year rolling maintenance programme to inspect, refurbish and replace these mechanical parts as necessary and has manufactured complete new plate train assemblies when the existing ones were deemed beyond economic repair.
All site works are normally carried out during night-time closures. This involves specific plate trains being removed and replaced with newly-refurbished elements. At the same time cleaning and inspection of beams, shelves, gullies and bearing blocks around the joint are undertaken.
Ekspan has a two-year rolling maintenance contract to inspect and maintain the joint on the Avonmouth Bridge
Plate trains are reassembled after refurbishment, ready to be fitted back into the joint on the next visit
Ekspan Ltd would like to thank Helena Russell (Editor – Bridge Design & Engineering) for kindly giving us permission to use this article.
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Regular maintenance of the roller shutter joint on one of the UK’s most heavily-trafficked structures is helping prevent disruption to the travelling public
Engineers will this month carry out the latest in a series of overnight, planned interventions to extend the service life of the roller shutter joint on the M5 Avonmouth Bridge in the west of England, and eliminate the need for more extensive maintenance works. Specialist Ekspan has been involved in maintenance and refurbishment of the expansion joints of the bridge for more than a decade; it is one of Highways England’s busiest structures.
The bridge, which is a strategic link to the south west of England, was opened in 1974. It is a 1.4km-long steel and concrete box structure with steel and concrete composite approach spans and steel main spans. It suffers substantial vibration compounded by the volume of traffic that crosses it daily — approximately 120,000 vehicles.
Worn plate trains are transported to the factory where they are dismantled to allow them to be cleaned, inspected, refurbished and shot-blasted, with new components being manufactured as necessary. Once the approved paint system has been applied, the plate trains are then reassembled ready to be fitted back into the joint on the next scheduled maintenance visit.
The benefit of planned preventative maintenance, associated with this type of expansion joint, reduces intervals for major works, and saves money by eliminating costly emergency works.